Not sure what has been mentioned so far, either in terms of description or photo.
Here are a few images of ice boats at work which are certainly post British Waterways, (i.e. post 1948),,,
TYCHO (which as has been pointed out still retains its ice ram to this day)....
The 1947 date in the captioning on this following one must be wrong. It is clearly post Nationalisation, as TYCHO is painted in British Waterways colours. One of the Oxford icebreakers is behind TYCHO.
Almost certainly SICKLE (my boat) Sorry for poor state of image - I have extracted several promises of access to an original over the years, but have been let down every time.
The livery, (an interpretation of which is what we currently have, dates this picture to no earlier than 1959, I think,
Edited to add RENTON
RENTON was converted to an ice boat in the same time frame as SEXTANS, SICKLE, THEOPHILsS and TYCHO, but what was added as an ice blade was very much massive than that added to the 4 Middle Northwich boats. It was still in place in the 1970s, and it is my understanding that when torched off it stayed on the boat as ballast. I'm told it can still be found in the hold....